The present invention relates to a system of analysis, which can be used in a mobile laboratory in a drilling site situation or in a similar situation, suitable for measuring (preferably in relation to at least two at least partially gaseous species, which derive preferably from a mixture extracted from a drilling mud, for example, methane, ethane, propane and/or any other heavier hydrocarbons) the quantities of the different isotopes of at least a same chemical element (preferably the quantities of 13C, carbon isotope with 6 protons and 7 neutrons, and of 12C, carbon isotope with 6 protons and 6 neutrons, respectively) by means of a laser isotopes analyser regulated for a single, at least partially gaseous species which contains said chemical element.
At the current state of the art, the instruments which are commonly used for measuring the isotope ratio of carbon in hydrocarbons, which is linked to the quantities in mass of the two isotopes mentioned, are mass spectrometers of the IRMS (isotope ratio mass spectrometer) type, which in fact allows for separate investigation of the relative concentration of stable isotopes, 12C and 13C, in different gaseous species. However, instruments of this type are not suitable for site analysis because of their dimensions and because they have to be used in particular environmental conditions free from vibrations and with stable temperature and pressure. These facts preclude their use in drilling sites, both on land and at sea, where said analysis has to take place in a continuous process.
The object of the present invention is that of producing a system of analysis which is able to measure the isotopic content of a chemical element, as a continuous process on site, and in relation to at least two different, partially gaseous species containing that element. Said species is contained in at least one partially gaseous mixture, which in turn was originally extracted, preferably from drilling mud. This allows accurate analyses to be carried out in a continuous and easily manageable manner, even in difficult environmental conditions, such as remote site locations on land or on a sea platform.
Another type of instrumentation for analysing the isotope ratio of carbon is known and described in patent application EP 1887342. This application is based on laser optical spectrometry, which allows the production of an instrument of simpler application and management and which can be used on site. However, because this instrument is configured in such a way that the laser spectrometer is able to quantify the relative abundance of the two stable isotopes of the carbon only in a single hydrocarbon species, it is not possible to analyse, the relative abundance of the two stable isotopes of the carbon also in other hydrocarbon species in a single analysis cycle and without modifying the configuration of the same laser spectrometer. In fact, the operation of changing the configuration of the analyzer leads to an unacceptable discrepancy between the analysis and the current depth.
Another object of the present invention is that of producing an instrument that is able to quantify the isotope ratio of a chemical element contained in at least two partially gaseous species in a continuous process on site. The partially gaseous species derive from a mixture previously contained in a drilling mud, without modifying the configuration of the isotope analyser. Thus, there is a good correlation between the analysis and the current depth. The latter analyser uses laser spectrometry and is intended to measure the relative quantity of two stable isotopes of a chemical element contained in each of said gaseous species. The gaseous species are previously separated from the mixture by means of a gas chromatograph controlled by software, and then transformed one by one into a gas species, such as carbon dioxide CO2, for which this analyser is configured. In this way, the isotope content of several gaseous species can be analysed, continuously and at different depths, without having to work on the analyser. Such an operation would take too much time for numerous analyses, which cannot be prolonged excessively because the analyses have to be correlated to the depth in approximate real time considering that the mixture flows continuously.
Moreover, at the state of the art, no site instrument for the analysis of the isotope ratio of carbon in hydrocarbon gases internally provides a system of chromatographic separation of each gaseous species constituting the mixture sampled and comprising a flame ionization detector or FID. This detector was introduced in order to check the correct separation of the single gas species, and therefore to define the correct sampling thereof before carrying out the analysis. Without the flame ionization detector, the instrument would be considered “blind” and therefore not able to ensure that the same gas species is sampled in every phase in which the analysis is to be performed.
A further object of the present invention is that of producing an instrument which is able to quantify, also in a continuous process on site, at least one isotope ratio of a chemical element contained in at least two partially gaseous species. The partially gaseous species derives from at least a mixture previously contained in drilling mud. The instrument is able to ensure that the gas species is exactly the same in every phase whereof in which the analysis is performed.
To date, it has not been possible to perform isotope analyses of continuous flows sufficiently in real time by means of laser isotopes analysers. This is because it was not possible to have sufficiently distanced times in sending a single gas species to said analyser so as to allow the laser isotope analysis. In any case, it was not possible to conclude the cycle of analysis in a sufficiently rapid manner for all the gaseous species of geological interest, which are usually methane, ethane and propane.
Therefore, an important object of the present invention is that of providing an instrument with which it is possible to send single gaseous species extracted from a mixture which flows continuously, to a laser analyser at sufficiently large intervals of time, and which can rapidly conclude the entire cycle of analysis for all the gaseous species of interest in order to perform several analyzes in real time. Thanks to the particular configuration given here to the gas chromatograph, the gaseous species to be analysed are sent to the isotope analyser at sufficiently distanced intervals of time, so as to allow the same to perform the analysis of each individual species. All the gas species not yet analysed remain trapped in a column of the gas chromatograph, while only one of these species is sent towards the analyser, in such a way as to obtain a sufficient interval of time between two successive analyses. In any case, the device takes a sufficiently reduced time to conclude the entire cycle of analysis of the gas species extracted at a certain depth, and in such a way that it is possible to perform analyses at many levels of depth.
On these bases, the present invention uses the technology known as gas chromatography for the separation of gaseous species, combined with a flame ionization detector (FID). The FID is intended to correctly identify the times of gas retention under investigation inside the various components of the gas chromatograph. Gas chromatography, together with laser spectrometry, is used to detect the isotopic content, and so the isotopic ratio, of the carbon contained in each of said gaseous species.